Manufacturing of semiconductor devices employs a thin gate dielectric (typically silicon dioxide) between the underlying silicon substrate and the gate electrode. Depositing a thin dielectric film on a silicon substrate forms a gate dielectric. Typical processes for growth of dielectric films include oxidation, chemical vapor deposition and atomic layer deposition processes. As integrated circuit devices shrink, the thickness of the gate dielectric needs to shrink proportionally. However, semiconductor manufacturers have reached the limit to which the thickness of conventional gate dielectric materials can be decreased without compromising the electrical characteristics. Rather than degrading the dielectric properties by using a silicon dioxide dielectric that is only a few atomic layers thick, equivalent dielectric performance can be achieved by substituting the silicon dioxide for a thicker layer of a new material exhibiting a higher dielectric constant. Therefore, new compositions or methods to produce a dielectric film with a higher dielectric constant than silicon dioxide (referred to as “high-k dielectrics”) are required. These “high-k dielectrics” must have a low leakage current through the gate dielectric. Thus, it is desirable to develop new compositions and methods of depositing dielectric films with the required higher dielectric properties so that films with more than one or two layers of atorns can be deposited. Due to the requirements for thin dielectric films, having uniform coverage of material that is very high quality is critical to the performance of the gate dielectric.
Depositing a thin metallic film, with the generic formula MxSiyNz, on a high-k film or a low-k film may be useful either as an electrode such as a gate electrode or a barrier layer. Typical processes for growth of metallic films include chemical vapor deposition, pulse chemical vapor deposition and atomic layer deposition processes. As integrated circuit devices shrink, the use of metal-based dielectric films raises issues relative to the compatibility of the use of these materials and polycrystalline silicon (poly-Si), so far used as a gate electrode. A new class of metal-based gate electrode is today considered to overcome issues such as depletion, cross-contamination. In DRAM, such metal electrode material is currently used.
The application of metal silicon nitrides as a barrier layer sandwiched between a Cu interconnect or electrode and a low-k dielectric film is another example of the application of compounds that contain metal and silicon. The metal nitrides have a good conductivity and can also effectively prevent contamination of low-k dielectric film by Cu. Moreover, the low resistance of the barrier layer is advantageous from the standpoint of lowering RC delay.
Metal silicon nitride films have heretofore been formed, for example, by CVD using ammonia and metal halide (e.g., TiCl4, TaCl5). This approach, however, requires a high thermal budget and a high process temperature (>650° C.) and is not compatible with back-end-of-line (BEOL) processes.
To overcome such drawbacks, it is known from U.S. Pat. No. 6,602,783 to use ammonia and an amino metal precursor (e.g., TDMAT, TDEAT, TBTDET, TAIMATA) for metal nitride film formation by CVD. The use of such amino metal precursors has been found to improve the film properties of, for example, CVD-TiSiN films. It has also been found that the formation of metal nitride film doped with small amounts of silicon by CVD using an amino metal precursor, silane SiH4, and ammonia is advantageous in terms of improving the barrier properties. SiH4, however, has a high vapor pressure and is pyrophoric:any SiH4 leak may be a safety issue. When, on the other hand, dialkylaminosilane Si(NR1R2)4 is used as the silicon source in place of silane, there is a strong likely hood of incorporation of large amounts of carbon into the film and of an increased barrier layer resistance.
Of particular interest is the formation of metal silicon oxynitride (“MSiON”) films, metal silicate (“MSiO”) or a metallic film (“MSiN”), which can be either a metal nitride, metal silicide, metal silicon nitride. Forming a MSiON or a MSiO dielectric or a metallic film typically involves feeding the relevant chemicals among a metal source, a silicon source, an oxygen source and a nitrogen source (collectively referred to herein as the “precursors”) in the proper relative amounts to a deposition device wherein a substrate is held at an elevated temperature. Forming the precursors are fed to a deposition chamber through a “delivery system.” A “delivery system” is the system of measuring and controlling the amounts of the various dielectric precursors being fed to the deposition chamber. Various delivery systems are known to one skilled in the art. Once in the deposition chamber, the dielectric precursors react to deposit a dielectric film on the silicon substrate in a “forming” step. A “forming” step or steps, as used in this application, is the step or steps wherein materials are deposited on the substrate or wherein the molecular composition or structure of the film on the substrate is modified. The “desired final composition” of the film is the precise chemical composition and atomic structure of the layer after the last forming step is complete. Compounds of hafnium, such as hafnium oxides, hafnium silicates and hafnium silicon oxynitrides are currently the most promising high-k gate dielectric choices. Compounds of tantalum, titanium and tungsten, either as metal nitride, metal silicide or metal silicon nitride are the most promising barrier or electrode materials. The metal source for the forming process is typically a liquid precursor or a liquid precursor solution containing the desired metal in a solvent. Similarly, the silicon sources available in the art prior to the current invention typically use a liquid precursor containing the desired silicon compound in a solvent.
It is disclosed, e.g. in Jpn. J. Appl. Phys., Vol. 42, No. 6A, pp. L578-L580, June 2003, Applied Physics Letters, Vol. 80, No. 13, pp. 2362-2364, April 2002, United States Published Applications 2003/0111678, 2003/0207549, or U.S. Pat. No. 06399208, Japanese patent application published as 2000272283, various processes to make dielectric films. However, all of these films suffer from one or more of the disadvantages discussed below.
Some gate dielectric-forming processes require multiple forming steps. For instance, a dielectric film may be formed by depositing a metal and silicon on a substrate in a first step followed by a second “post deposition step” wherein the composition or structure of the deposited metal/silicon film is modified to achieve the desired final composition of a MSiON gate dielectric film. An example of a post deposition step is rapid thermal annealing in an environment that is filled of nitrogen or ammonia. Because control of the film composition is important in dielectric film deposition processes, the fewer the steps, the better the control of the process, and the higher the quality (reflected by dielectric constant, density, contamination, composition and other quality control properties) and conformality (the ability of the film to evenly deposit on all surfaces and shapes of substrate) of the dielectric film.
It is known in the art that any silicon sources that contain carbon in the ligands can lead to carbon in the film and result in degraded electrical properties, either enhancing the leakage current for insulating films or reducing the conductivity for metallic films. Furthermore, chlorine incorporated in the films is undesirable due to its harmful effect on the electrical properties of the film and the stability of the chlorine in the film (the stability makes it hard to remove chlorine from the dielectric film). Also, the presence of chlorine in the silicon or metal source generates chloride based particulates in the reaction chamber and deposits in the exhaust system. Thus, to achieve the ideal electrical properties and to minimize particulate generation and tool downtime due to exhaust system cleaning, it is desirable to deposit dielectric films from precursors free of carbon or chlorine in the atomic structure.
The physical properties of a film may be modified by the metal (M) to silicon (Si) ratio, or (M/Si). It is desirable to control the M/Si ratio over a broad range. Thus, it is important to be able to vary the metal and silicon feed independently to achieve the broadest possible M/Si ratios. Some processes use a silicon source precursor that also contains some amount of the metal to be deposited. However, that changes in the metal-containing silicon source precursor feed rate changes the total amount of the metal fed to the process (due to the metal contained in the silicon precursor). This limits the controllability of the deposition process because the silicon feed rate cannot be changed without changing the total amount of metal being fed to the deposition chamber. Furthermore, the ratio of M/Si that can be fed is limited by the composition of the metal in the silicon source precursor. Thus a change in the desired M/Si ratio may require changing precursor solutions being fed to the process.
Vaporizing silicon precursor streams can also lead to problems with film composition control. Some processes in the art use a vaporizer to vaporize the liquid silicon source. The vaporized stream is then fed to the deposition chamber. When the metal source and the silicon source are supplied in liquid form, they must both be vaporized before being introduced into the deposition chamber. Vaporizing two different streams can lead to variable feed concentrations and formation of silicon or metal residues in the vaporizer that can adversely affect the conformality of the film composition. Differences in vaporization of the silicon and metal sources can also lead to compositional gradients in the dielectric.
Bubbling a carrier gas through a liquid precursor can also cause quality problems. In some processes, a silicon source is fed by bubbling a carrier gas through a liquid silicon source. A vaporizer is not used in these processes because the vapor pressure of the silicon source is high enough to be transported as a vapor in a mixture with the carrier gas. In these processes, the composition of the stream transporting the silicon source to the deposition chamber can vary with temperature and pressure in the bubbling system. This variability in stream composition leads to variability in the composition of the dielectric film, which is a significant quality control issue.
For the foregoing reasons, it is desirable to form a film of the final desired composition in a single forming step. Furthermore, the film should minimize chlorine and carbon content in the molecular structure. It is also desirable to use a silicon source that is free of any deposition metals so the silicon source feed and the metal source feed may be independently controlled. Finally, it is desirable to have a silicon source that is in the vapor phase at process feed conditions to avoid the need to vaporize a liquid silicon source or bubble a carrier gas through a liquid source.